1. Field of the Invention
The present invention relates to a label printing machine, and more particularly to an ink supply device for the printing head of a label printing machine.
2. Description of the Prior Art
A conventional tagging or label printing machine of the desk type has an ink supply device comprising an ink roller that is attached rotatably to the leading ends of of spring-biased pivotable arms, so that the surface of the ink roller is depressed as it rolls over the type surfaces of the printing head in accordance with the pivot positions of the arms, thereby to supply the type surfaces with ink.
However, such a conventional ink supply device has several disadvantages.
The ink roller is urged into contact with the type surfaces by a spring. The pressure of the ink roller upon the type surfaces will gradually decrease as the biasing force of the spring is weakened due to its aging. Ink application gradually diminishes so that the imprints upon the label surfaces become unclear.
Even those labels which are not clearly printed by conventional label printing machines are still accepted for use as price-indicating labels so long as they can be read by the naked eye when a customer purchases a commodity or when a clerk of a store totals the sale. During this decade, however, the so-called "POS (Point-of-Sale) System" has been put into practice worldwide. In this system, machine readable bar codes or OCR characters are printed on tags or labels are are automatically read out by an optical reader that is connected to an electronic computer. These readers are used in place of the register clerk for reading the labels on the commodities. These readers permit the materials for management, such as stock, sale, market research and profit counting, to be stored for subsequent processing by the computer. For such a system, precision in the imprints upon the labels, or the like, is required.
Moreover, as the biasing force of the spring that presses an inking roller against the type surfaces is gradually weakened, the ink roller is less depressed by the types of the printing head and the ink stored at the center of the ink roller fails to ooze out. As a result, ink impregnated in the ink roller that is not in the vicinity of the periphery of the ink roller will not be squeezed from the ink roller. This reduces the number of labels that can be printed by a single ink roller, thus rendering conventional ink supply devices uneconomical.
Still further, in a conventional desk type label printing or tagging machine, the rotating arms for holding the ink rollers, as well as the cover of the machine, protrude considerably from the side of the body of the machine because the rotating arms normally rotate sideways of the body so as to apply ink to the type surfaces. The protrusions will often hinder the label printing and/or applying operations, with resultant deterioration in design.